The U.S. fertility rate just hit a historic low. Why some demographers are freaking out.

Birthrates are declining for teens and women in their 20s — and rising for women in their 30s and 40s. (iStock)

The United States is in the midst of what some worry is a baby crisis. The number of women giving birth has been declining for years and just hit a historic low. If the trend continues — and experts disagree on whether it will — the country could face economic and cultural turmoil.

According to provisional 2016 population data released by the Centers for Disease Control and Prevention on Friday, the number of births fell 1 percent from a year earlier, bringing the general fertility rate to 62.0 births per 1,000 women ages 15 to 44. The trend is being driven by a decline in birthrates for teens and 20-somethings. The birthrate for women in their 30s and 40s increased — but not enough to make up for the lower numbers in their younger peers.

A country's birthrate is among the most important measures of demographic health. The number needs to be within a certain range, called the “replacement level,” to keep a population stable so that it neither grows nor shrinks. If too low, there's a danger that we wouldn't be able to replace the aging workforce and have enough tax revenue to keep the economy stable. Countries such as France and Japan that have low birthrates have put pro-family policies into place to try to encourage couples to have babies. The flip side can also be a problem. Birthrates that are too high can strain resources such as clean water, food, shelter and social services, problems faced by India, where the fertility rate has fallen over the past few decades but still remains high.

The debate now is about whether the United States is headed toward a “national emergency,” as some have feared, or whether this is a blip and the birthrate will level off soon.

“It's about millennials,” says Donna M. Strobino, a professor of population, family and reproductive health at the Johns Hopkins Bloomberg School of Public Health.

Here's a look at some surprising takeaways from recent research about the sex lives of the millennial generation. (Claritza Jimenez/The Washington Post)

Those supposedly entitled young adults with fragile egos who live in their parents' basements and hop from job-to-job — it turns out they're also much less likely to have babies, at least so far. Some experts think millennials are just postponing parenthood while others fear they're choosing not to have children at all.

Strobino is among those who is optimistic and sees hope in the data. She points out that the fall in birthrates in teens — an age when many pregnancies tend to be unplanned — is something we want and that the highest birthrates are now among women 25 to 34 years of age.

“What this is is a trend of women becoming more educated and more mature. I’m not sure that’s bad,” she explained.

Indeed, as fertility treatments have extended the age of childbearing, the birthrates among women who are age 40 to 44 are also rising.

(National Vital Statistics System)

William Frey, a demographer and senior fellow at the Brookings Institution, points out that despite the recent decline, the U.S. fertility rate still remains relatively high compared to many other developed countries like Germany and Italy. The United States also still has more births than deaths. And we still have a growing labor force. All these things mean, he said, “I don’t think that’s cause for alarm.”

Frey attributed the decline in birthrates to a women's “lifestyle” choice as well as the fact the economy has been in a funk. Times of economic downturn or uncertainty tend to cause a drop in birthrates, but when things turn around they tend to bounce back in a kind of catch-up period.

“Every year I say when the economy is getting better then we’ll start having more children,” he said, “and I'm still expecting that to happen.”

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